The present invention relates to a lever tumbler lock of the kind in which the scrape marks created by the key bit as it displaces the various tumblers will not reveal completely the configuration of the key bit, these scrape marks being readable with the aid of fibre optics.
A tumbler lock of this kind is known from SE-B-8601831-4. By the arrangement of special recesses in the ends of the camming surfaces of respective tumblers, the scrape marks created by rotation of the key bit on the tumbler camming surfaces for some cam holders can be caused to start and finish at mutually the same locations on respective cam surfaces. This means that such scrape marks will no longer reveal information as to the construction of corresponding parts of the key bit. Due to the abutment of the side surfaces of the key bit with the cam surfaces, this particular lock construction results in the application of relatively large lateral forces on certain of the tumblers, which subject the tumbler guide pins to load and therewith render the key more difficult to turn than in the case of conventional tumbler lock construction.